The invention relates generally to the fields of particle detectors and antennas, and, more particularly, to an integrated particle detector and electromagnetic antenna apparatus that provides a large aperture for efficient collection of charged particles and electromagnetic radiation and transmission of electromagnetic radiation.
Space physics is the science concerned with the study of the plasmas or collections of charged particles such as ions and electrons that are encountered in space. One of the methods used in the study of plasmas is the in-situ analysis of the particles according to their energy, mass, and charge. The instruments used to determine these plasma parameters include energy-per-charge analyzers, mass-per-charge analyzers, magnetic or time-of-flight mass spectrometers, and instrumentation based on the energy loss in matter. One of the important parameters of particle analyzer instrumentation is the sensitivity, which is related to the geometric factor G.sub.i, which in turn is related to the collection area. Therefore, one way to increase the sensitivity of the plasma instrumentation is to increase the collection or aperture area. There has indeed been a trend toward larger instruments with larger geometric factors.
To understand the measurement process in particle instrumentation, consider the relationship between the particle distribution function f.sub.i (E) for particle species i and the telemetered quantities of detector count rate C.sub.i, particle energy E, and mass M.sub.i : EQU f.sub.i (E)=C.sub.i M.sub.i.sup.2 /(G.sub.i E.sup.2)s.sup.3 m.sup.-6 !.
The factor G.sub.i is the energy-geometric factor, which is approximately constant with energy for a given instrument and particle species. The value G.sub.i expresses the instrument response in terms of its sensitive area A, its angular acceptance .OMEGA., energy acceptance .DELTA.E/E, detector efficiency .epsilon..sub.i, and the grid transmission T. In general, G.sub.i may be written as EQU G.sub.i =A.OMEGA.T.epsilon..sub.i (.DELTA.E/E)m.sup.2 sr!,
where .OMEGA. represents the averaged angular response and .DELTA.E/E represents the averaged energy response normalized to the energy of the central particle trajectory.
The quality of the measurement f.sub.i (E) is thus seen to be determined by the minimum detectable count rate and by the instrumental constant G.sub.i. Because the limiting minimum detectable count rate is set by detector noise and by the background due to high energy radiation in the space environment, the only practical way to make an instrument more sensitive to f.sub.i (E) is to increase the size of the constant G.sub.i. G.sub.i is increased by increasing the area A, the acceptance angle .OMEGA., the detector efficiency .epsilon..sub.i, or the grid transmission T. The present invention is mainly concerned with increasing the collection area A.
In applications involving plasma particle detection in space, there is a need for having a large collection area for collecting as many particles as possible in the tenuous medium in order to increase sensitivity and to allow for shorter integration times. For example, the density of the solar wind decays with the radial distance r from the Sun by the inverse square law, or 1/r.sup.2. For an instrument in the outer solar system to have the same sensitivity as at one astronomical unit, or the mean distance from the Earth to the Sun, its collection area needs to be increased by a similar factor. Also, the solar wind consists largely of ionized hydrogen, mixed with about four percent of ionized helium and fewer ions of heavier elements. An increase in the collection area of the instrumentation beyond that currently being flown on spacecraft would improve the sensitivity and thereby the temporal resolution for the detection of ions comprising a small population of the solar wind.
Large particle collectors have been fielded in the past. However, these detectors were flat, passive metal foils with no concentrator. The foils were required to be retrieved and returned to Earth for analysis in the laboratory. The present invention, however, uses a large collection area and focuses particles on a sensor. The sensor can be an active sensor for in-situ analysis of the collected particles.
Recently, the paradigm has shifted in space research from a few comprehensive missions to a greater number of more narrowly focused missions. At the same time, cost had to be reduced, leading to an emphasis on "faster, better, and cheaper" missions. As a consequence, new missions require smaller, yet more capable and sensitive instrumentation. This has lead to a higher degree of integration of the spacecraft and its subsystems.
One of the largest structural elements of a spacecraft is its high-gain antenna, which often consists of a parabolic dish. This is particularly true for interplanetary spacecraft. With the move towards miniaturization and cost reduction, it is undesirable to have two large separate collectors on the spacecraft, one for electromagnetic radiation and one for particles.
For the foregoing reasons, there is a need for a large particle collector device that can provide high particle collection sensitivity and be integrated with a large electromagnetic collector device resulting in reduced cost and spacecraft size.